Field of the Invention
This invention relates generally to a lifting tool for lifting a rotor coupled to a generator so as to allow a rotor bearing to be removed from under the rotor and, more particularly, to a lifting tool for lifting a generator rotor so as to allow a rotor bearing to be removed from under the rotor, where the tool is bolted to a bearing pedestal, and where the tool includes a hydraulic ram that lifts the rotor and a pair of jack screws that hold the lifted rotor.
Discussion of the Related Art
High voltage generators for generating electricity as a power source are well known in the art. A power plant may be a nuclear or fossil heat source that rotates a turbine shaft by the expansion of a working gaseous fluid across turbine blades that in turn cause the shaft to rotate. The turbine shaft is coupled to an input shaft of a high voltage generator that is mounted to a rotor having a special configuration of coils. An electrical current provided in the rotor coils generates a magnetic flux around the coils, and as the rotor rotates, the magnetic flux interacts with windings in a stator core enclosing the rotor, which generates a current flow in the windings.
In one power plant type the generator rotor extends from the generator and is coupled to the turbine shaft. The generator rotor is supported by and extends through a rotor bearing, which is an annular bulk of metal having a central bore with an inner surface on which the rotor rotates.
The rotor bearing is mounted within a bearing housing that is part of a bearing pedestal supported on the turbine foundation. Oil is pumped into the bearing housing, which provides a film of oil on the inner surface of the bore that slightly lifts the rotor relative thereto, thus allowing the rotor to effortlessly turn within the bore.
The generator requires periodic maintenance where the generator is shut down and various maintenance procedures are performed, such as cleaning, wear detection, part replacement, part inspection, etc. Some of these maintenance procedures require that the rotor bearing be removed from the bearing housing and inspected and possibly replaced. This generally requires partial disassembly of the pedestal including removal of a housing cap, end seals, etc. from the housing to expose the bearing. A typical rotor bearing of this type will include two bearing half sections, where a bottom bearing half section sits below the rotor and a top bearing half section is exposed when the housing cap is removed. The top half section is first removed from the rotor, and the bottom half section is then rotated around the rotor and subsequently removed.
During removal and inspection of the bearing, the weight of the rotor is resting on the bottom bearing half section, which prevents it from being easily removed. Thus, the rotor needs to be slightly lifted off of the bottom half section. One known procedure for lifting the rotor includes mounting a saddle and jack screw tool to the rotor proximate to the bearing pedestal. The saddle includes a pair of legs that are mounted on the turbine foundation and a cross-member that includes a jack screw. Once the cross-member is positioned below the rotor, the jack screw is used to apply lifting pressure to the rotor to lift the rotor off of the bottom bearing half section and hold it in the lifted position.
The saddle and jack screw tool referred to above is a large and robust device that requires significant room to be properly deployed. However, for certain generator designs, there is not enough space around the bearing pedestal to position the tool, which thus requires that many large, heavy and complex components to be disassembled and removed to make room for the tool. Further, the turbine foundation may be elevated or awkwardly shaped, which requires special supports to be used in connection with the tool. Thus, there is a need in the art for a lifting tool for lifting the rotor that is better able to accommodate the generator environment.